1. Field
The present invention generally relates to data compression and decompression in a communication system and, in particular, to a system and method for optimizing Robust Header Compression (ROHC) in a high delay variance environment.
2. Background
ROHC is an Internet Engineering Task Force (IETF) header compression framework that provides for high efficiency and robustness in wireless communication systems. Among other features, ROHC supports Real-time Transfer Protocol/User Datagram Protocol/Internet Protocol (RTP/UDP/IP) and UDP/IP compression profiles. The ROHC working group is also specifying support for a Transmission Control Protocol/Internet Protocol (TCP/IP) compression profile.
ROHC exhibits robustness, i.e., the ability to tolerate errors on the wireless links. ROHC is useable with multi-media applications and provides for header compression for various applications and protocols. Header compression is a technique to reduce the header size transmitted over a link thereby increasing the link efficiency and throughput. Header compression is particularly useful on slow links or when packet sizes are small where a reduction in the header size results in a significant decrease in the header overhead. Header compression achieves this by leveraging header field redundancies in packets belonging to the same flow. In particular, many packet header fields such as IP source and destination addresses remain constant throughout the duration of a flow while other fields such as sequence numbers change predictably to allow header compression to transmit only a few bytes of header information per packet.
FIG. 1 illustrates a typical ROHC compression/decompression block diagram 100 of IPIJUDP/RTP headers over a communication link. Typically, reference copies of the full headers are stored at a ROHC compressor 102 and a ROHC decompressor 104 in order to reliably communicate and reconstruct original packet headers. RFC 3095, available at URL www.fags.org/rfcs/rfc3095.html, which is fully incorporated herein by reference, allows the ROHC decompressor to notify the compressor about jitter (delay variance) seen by a received packet on the link between the compressor-decompressor (comp-decomp) using a JITTER option sent with a FEEDBACK packet. Subsequently, the JITTER option may be used by the compressor to estimate the number of bits required to compress the RTP Timestamp (RTP TS) field when using a timer-based compression method. It is appreciated, however, that sending the JITTER option for every packet may introduce a significant overhead on the feedback channel and its use should be optimized. Accordingly, there is a need in the art for a system and method for optimizing ROHC in a high delay variance environment.